feat: HorizontalRunnerAutoscaler Webhook server (#282)

* feat: HorizontalRunnerAutoscaler Webhook server

This introduces a Webhook server that responds GitHub `check_run`, `pull_request`, and `push` events by scaling up matched HorizontalRunnerAutoscaler by 1 replica. This allows you to immediately add "resource slack" for future GitHub Actions job runs, without waiting next sync period to add insufficient runners.

This feature is highly inspired by https://github.com/philips-labs/terraform-aws-github-runner. terraform-aws-github-runner can manage one set of runners per deployment, where actions-runner-controller with this feature can manage as many sets of runners as you declare with HorizontalRunnerAutoscaler and RunnerDeployment pairs.

On each GitHub event received, the webhook server queries repository-wide and organizational runners from the cluster and searches for the single target to scale up. The webhook server tries to match HorizontalRunnerAutoscaler.Spec.ScaleUpTriggers[].GitHubEvent.[CheckRun|Push|PullRequest] against the event and if it finds only one HRA, it is the scale target. If none or two or more targets are found for repository-wide runners, it does the same on organizational runners.

Changes:

* Fix integration test
* Update manifests
* chart: Add support for github webhook server
* dockerfile: Include github-webhook-server binary
* Do not import unversioned go-github
* Update README

github/fake/fake.go

@@ -24,6 +24,16 @@ const (
 `
 )
 
+type ListRunnersHandler struct {
+	Status int
+	Body   string
+}
+
+func (h *ListRunnersHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	w.WriteHeader(h.Status)
+	fmt.Fprintf(w, h.Body)
+}
+
 type Handler struct {
 	Status int
 	Body   string
@@ -94,10 +104,7 @@ func NewServer(opts ...Option) *httptest.Server {
 		},
 
 		// For ListRunners
-		"/repos/test/valid/actions/runners": &Handler{
-			Status: http.StatusOK,
-			Body:   RunnersListBody,
-		},
+		"/repos/test/valid/actions/runners": config.FixedResponses.ListRunners,
 		"/repos/test/invalid/actions/runners": &Handler{
 			Status: http.StatusNoContent,
 			Body:   "",
@@ -159,3 +166,10 @@ func NewServer(opts ...Option) *httptest.Server {
 
 	return httptest.NewServer(mux)
 }
+
+func DefaultListRunnersHandler() *ListRunnersHandler {
+	return &ListRunnersHandler{
+		Status: http.StatusOK,
+		Body:   RunnersListBody,
+	}
+}

github/fake/options.go

@@ -1,8 +1,11 @@
 package fake
 
+import "net/http"
+
 type FixedResponses struct {
 	ListRepositoryWorkflowRuns *Handler
 	ListWorkflowJobs           *MapHandler
+	ListRunners                http.Handler
 }
 
 type Option func(*ServerConfig)
@@ -25,6 +28,15 @@ func WithListWorkflowJobsResponse(status int, bodies map[int]string) Option {
 	}
 }
 
+func WithListRunnersResponse(status int, body string) Option {
+	return func(c *ServerConfig) {
+		c.FixedResponses.ListRunners = &ListRunnersHandler{
+			Status: status,
+			Body:   body,
+		}
+	}
+}
+
 func WithFixedResponses(responses *FixedResponses) Option {
 	return func(c *ServerConfig) {
 		c.FixedResponses = responses

github/fake/runners.go

@@ -29,15 +29,15 @@ func (r *RunnersList) Add(runner *github.Runner) {
 func (r *RunnersList) GetServer() *httptest.Server {
 	router := mux.NewRouter()
 
-	router.Handle("/repos/{owner}/{repo}/actions/runners", r.handleList())
+	router.Handle("/repos/{owner}/{repo}/actions/runners", r.HandleList())
 	router.Handle("/repos/{owner}/{repo}/actions/runners/{id}", r.handleRemove())
-	router.Handle("/orgs/{org}/actions/runners", r.handleList())
+	router.Handle("/orgs/{org}/actions/runners", r.HandleList())
 	router.Handle("/orgs/{org}/actions/runners/{id}", r.handleRemove())
 
 	return httptest.NewServer(router)
 }
 
-func (r *RunnersList) handleList() http.HandlerFunc {
+func (r *RunnersList) HandleList() http.HandlerFunc {
 	return func(w http.ResponseWriter, res *http.Request) {
 		j, err := json.Marshal(github.Runners{
 			TotalCount: len(r.runners),

github/github_test.go

@@ -32,7 +32,10 @@ func newTestClient() *Client {
 }
 
 func TestMain(m *testing.M) {
-	server = fake.NewServer()
+	res := &fake.FixedResponses{
+		ListRunners: fake.DefaultListRunnersHandler(),
+	}
+	server = fake.NewServer(fake.WithFixedResponses(res))
 	defer server.Close()
 	m.Run()
 }